The present invention relates generally to detectable security markings. More specifically, the present invention relates to optically encoded markings, formed from at least one emitter and at least one absorber, that exhibit a first emission in response to a first excitation of the emitter and a change in that emission in response to excitation of the absorber such that various combinations of emitter and absorber materials create a machine readable response that cannot be detected by the human eye.
Counterfeiting and forgery have become significant concerns in the modern economy and marketplace. While fraudulent activities such as counterfeiting currency and forging signatures or handwriting are common, methods of creating and perfecting forgeries and counterfeit documents have become easier and more available with the advent of highly skilled computer printing and processing. Given the advances and reduction in cost of computing technology and printing techniques, the incidence of forgeries, counterfeited documents, and other fraudulent activities have increased. This is problematic in that countless areas of today's high-technology society require and rely upon certification, authentication and protection of highly valuable documents, papers, currency or other materials in order to prevent fraud and counterfeiting.
A similar problem exists in a variety of contexts. In addition to protecting against counterfeit currency, authentication of valuable documents or materials also affects many facets of the economy. Authentication stamps such as visas or postmarks, for example are subject to fraudulent use and forgery. Also a wide variety of products and consumer goods may be created as knock-offs cheap replacements or gray market goods. Notaries public use a raised stamp to authenticate notarized documents. Drivers' licenses, passports and other photographic identification contain holograms and microprinting. Sporting memorabilia and retail clothiers use holographic tags and stamps to assist in proving authenticity. Even fashion designers are now including authentication devices in their clothing to prevent passing off of knock-offs as designer products.
A disadvantage to most of the traditional security features is that they are visible and known to the world. If a counterfeiter is aware there is a security thread in a bill or a watermark in a document, replication of the security feature is easier. Once a feature is made known to the public, a counterfeiter may begin to develop specific strategies and solutions to overcome the security protections provided by the specific feature.
As a result, for ensuring authenticity to certain documents, specific inks have been developed. These inks incorporate colorless products, i.e. invisible to the naked eye in visible light, but which can be observed by illuminating them with a light having a particular wavelength, such as ultraviolet, which gives rise to fluorescence or phosphorescence of the ink in turn making them visible, or by making them react with other products rendering them visible to the naked eye. Typically, as the exposure to the particular light (UV) stops and after a very short time, the ink reassumes its initial, invisible appearance. The type of compound responsible for this phenomenon absorbs light at a certain wavelength and reemits it at a higher wavelength for the exposure time.
More recently, products that change absorption spectrum under the effect of light have appeared. These products are called photochromic inks. Generally, said photochromic inks are invisible under normal illumination conditions and become visible, i.e. having e.g. a blue or green color, following illumination under ultraviolet light. Thus, for example, a document on which inscriptions are made with blue or green ink on a background covered by a photochromic ink cannot be photocopied. Thus, when the document is exposed to the radiation of the photocopier, the background of the document is tinted blue or green and the inscriptions made with normal ink can no longer be distinguished from the background. Similarly, thermochromic inks are used as authentication marks. Like photochromic inks, thermochromic inks are invisible under normal conditions and become visible, i.e. having e.g. a blue or green color, when a heat source is applied. The difficulty in the use of these materials is that they operate only to change an absorption response. Since the changes are intended to be very subtle and not visually detectable, this creates the need to introduce probes that create an illumination at the spectral band of interest in order to determine if the absorption change is occurring.
The difficulty of all of these technologies is that their responses are limited and once their function and placement is known a counterfeiter can replicate them without great difficulty.
Accordingly, there is a need for covert optically encoded markings, formed from at least one emitter and at least one absorber, that exhibit a first emission in response to a first excitation of the emitter and a change in that emission in response to excitation of the absorber such that various combinations of emitter and absorber materials create a machine readable response that cannot be detected by the human eye.